The invention relates to a method for controlling an automatic switch-off and switch-on procedure of a drive unit in a motor vehicle using a start-stop device.
In order to reduce fuel consumption and pollutant emissions, methods and systems are currently being developed and partly already in use which automatically switch off the internal-combustion engine of a motor vehicle under certain conditions or if preset switch-off conditions exist, and automatically switch it on again if preset switch-on conditions or switch-on requests exist. Such methods and systems, often referred to as start-stop devices, are suitable mainly for city traffic for reducing fuel consumption because, in city traffic, the vehicle often comes to a stop at traffic lights or as a result of traffic, and the operation of the internal-combustion engine is not required.
Thus, an automatic stop-and-start control device for an internal-combustion engine is known from German Patent document DE 101 61 343 A1, wherein the control device carries out corresponding measures for switching off the internal-combustion engine if all mentioned switch-off conditions have been met. For example, the speed of the vehicle has to be below a given limit value; no gear should be engaged in the case of manual transmissions; and, in the case of automatic-transmission vehicles, the gear shift position of the transmission should be in neutral.
Furthermore, German Patent document DE 100 30 290 A1 also discloses a method and a system for the automatic switching-off and restarting of an internal-combustion engine. In this case, an automatic switch-off is prevented when the charge state of the battery of the vehicle is below a preset blocking threshold. As further switch-off conditions, it is also checked whether the vehicle speed is below a preset limit value, whether the transmission is idling and whether the gas pedal is in an inoperative position. A switching-on of the drive unit takes place as soon as a switch-on request is present.
Currently, systems are still in the research stage which link vehicles mutually and with their surroundings by way of a communications channel. Thus, for example, traffic lights equipped with this technology can transmit their current state and a forecast of the point-in-time of their next change of state. A vehicle receiving these data can then generate a corresponding display or directly intervene in the drive control corresponding to the data.
When an above-mentioned automatic start-stop system is used, it is contemplated that the driver stops at a traffic light and disengages the gear, whereupon the engine is automatically switched off although the traffic light changes back to green shortly thereafter. Many drivers therefore now try to release the accelerator early when a red light is recognized in order to roll toward the traffic light while coasting. However, since the change of state of the traffic light is unknown, an optimal—favorable with respect to consumption—drive control is often difficult for the driver. This is further influenced by the presence of additional vehicles in one's own traffic lane.
German Patent document DE 202004003215U1 discloses a start-stop system wherein the traffic light state data are taken into account such that a holding duration is estimated and, as a function of the forecast, an automatic stop is initiated or prevented.
From European Patent document EP 1 475 265 B1, a method of operating a vehicle is known whereby, as a function of detected objects (including traffic lights), the speed and the operating mode of the engine is automatically adapted. Furthermore, the publication “Potentials of Forward Looking Driver Assistance in Reduction of Fuel Consumption” by Neunzig and Benmimoun, 2002, also indicates various concepts for reducing consumption while taking into account many different environmental data. In particular, in this case, the speed is correspondingly adapted as a function of the available vehicle-external data or the engine is switched off.
It is an object of the invention to provide an improved method for controlling an automatic switch-off and switch-on procedure of a drive unit in a motor vehicle with respect to an automatic switch-on procedure which is optimal with regard to consumption and comfort.
This and other objects are achieved by a method of controlling an automatic switch-off and switch-on procedure of a drive unit in a motor vehicle by use of a start-stop device, by which, when the motor vehicle stops, the drive unit is automatically switched off if predefined switch-off conditions have been met, and by which an automatically switched-off drive unit is automatically switched on if at least one driver-side or system-side switch-on request is made. When a system-side switch-on request takes place, the automatic switch-on procedure will be suppressed at least temporarily if a delay condition exists.
The invention starts out from a conventional method of controlling an automatic switch-off and switch-on procedure of a drive unit in a motor vehicle by way of a start-stop device, by which, when the motor vehicle stops, the drive unit is automatically switched off if predefined switch-off conditions have been met, and by which an automatically switched-off drive unit is automatically switched on if at least one driver-side or system-side switch-on request is made. A driver-side switch-on request is a driver's measure by which he expresses his intension to continue his drive again. This may, for example, be the operation of a clutch for engaging a gear. A system-side switch-on request may take place, for example, when no sufficient air conditioning of the vehicle can be ensured or if the charge state of the battery has fallen below a given threshold or if, in the case of a further discharge, there is the risk that a start can no longer be initiated.
The invention is now based on the problem that, when a drive unit is automatically switched off, a situation may arise that the voltage supply will be strained by active consuming devices, as, for example, the radio, during the stoppage, to such an extent that a system-side switch-on request for starting the drive unit is generated and is sent to the start-stop system in order to prevent a further discharging of the battery. The start-stop system will then automatically restart the engine. On the one hand, this may irritate the driver because he will not know why the drive unit is being restarted and, on the other hand, the preferred automatic start may be unnecessary because the driver would initiate the start anyhow in certain situations and the battery would then be charged.
In order to avoid this problem, it is within the scope of the method of the invention that, when a system-side switch-on request takes place, the automatic switch-on procedure will be suppressed at least temporarily if a delay condition is present; thus, it is initiated in a delayed manner, if required, or is initiated only if a driver-side switch-on request is present.
Since a system-side switch-on request will often take place when an optimal operation of the vehicle in the case of a significantly longer stoppage of the engine can no longer be sufficiently guaranteed, in an advantageous further development of the invention, a delay condition may exist if a driver-side switch-on request is to be expected within a predefined time interval after the system-side switch-on request and/or if an automatic start of the drive unit as a result of a driver assistance system, particularly a cruise control system (for example, a so-called ACC Stop & Go), is to be expected within a predefined time interval. In this case, the time interval may be the same for all system-side switch-on requests, or may be preset individually for every switch-on request. If a driver-side switch-on request and/or the automatic start as a result of a driver assistance system is to be expected in the near future, the start may possibly still be delayed because the threshold values, at whose reaching or falling-below, a system-side start request is emitted, are as a rule selected such that no critical condition of the vehicle will be reached yet if the stoppage time of the engine is slightly longer. If the expected point-in-time of a driver-side switch-on request and/or of the automatic start as a result of a driver assistance system is within the predefined time interval, a suppression of the automatic start will be possible until the actual implementation of the driver-side switch-on request. If, however, the point-in-time that is to be expected of the driver-side switch-on request and/or of the automatic start as a result of a driver assistance system is outside the time interval, the drive unit has to be started immediately because otherwise an optimal operation of the vehicle may possibly no longer be guaranteed.
The point-in-time that is to be expected of a driver-side switch-on request and/or of the automatic start as a result of a driver assistance system can be determined as a function of many different data. Advantageously, the point-in-time, that is to be expected, of a driver-side switch-on request and/or of the automatic start as a result of a driver assistance system, while the drive unit is switched off, is determined as a function of predefined operating values of the motor vehicle, state variables of the motor vehicle, and/or other parameters of the motor vehicle. If, for example, while the drive unit was automatically switched-off, the front passenger door or the trunk was opened, the conclusion can be drawn, when the trunk or the front passenger door are closed, that the entering/exiting/loading or unloading operation has been concluded and the driver would like to soon start driving again.
As an alternative or in addition, the point-in-time, that is to be expected, of a driver-side switch-on request and/or of the automatic start as a result of a driver assistance system, when the drive unit is switched off, can also be determined as a function of vehicle-external information, particularly of data of other traffic participants or concerning other traffic participants, environmental data, and/or traffic engineering data. The traffic engineering data may particularly comprise data of traffic light systems which contain information concerning the point-in-time of a change of state. If it is recognized, for example, by means of traffic engineering data that the traffic light will switch back to green in the foreseeable future, it can be assumed that the driver will soon want to start driving. Thus, an automatic start of the drive unit, which is to be carried out on the basis of a system-side switch-on request, can be delayed or can be prevented pending the arrival of a driver-side switch-on request. The vehicle-external information can be determined and/or made available by a navigation system, an image-reproducing environment monitoring system, a traffic engineering communications system, and/or a car-to-car communications system.
By means of the above-mentioned vehicle information and/or the vehicle-external data, not only the point-in-time of the initiation of an automatic start but also the carrying-out of a switch-off procedure can be influenced. In order to be able to ensure, for example, a sufficient stoppage time until a switch-on request takes place, it may be that, before the initiation of an automatic switch-off procedure of the drive unit, a stoppage duration of the drive unit is forecast that is possible when taking into account current operating values of the vehicle, state variables of the vehicle, other parameters of the vehicle, and/or vehicle-external information or data. If all other switch-off conditions have been met, an automatic switch-off procedure will then be permitted or prevented as a function of the forecast stopping duration. Therefore, if all other switch-off conditions have been met, an automatic switch-off procedure is advantageously initiated if the forecast stopping duration is at least no less than a predefined stopping duration limit value, which, if necessary, may also be variable. If the forecast stopping duration is less than the possibly freely applicable stopping duration limit, however, no automatic switch-off procedure will be permitted.
If the vehicle is additionally equipped with a cruise control system, the speed can also be adapted correspondingly while the above-mentioned vehicle-external data are taken into account, so that the consumption will be favorable. In particular, when the vehicle approaches a traffic light, the speed in the run-up can be correspondingly adapted, so that, at the point-in-time of the light change to green, the vehicle can easily continue to drive.
The method according to the invention as well as its advantageous further developments can be implemented by way of an implemented algorithm or a corresponding module arrangement in a control device provided for this purpose, particularly in an engine control unit or an air-conditioning control unit.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.